This invention relates to hydroforming apparatus and more particularly to devices for locating a tubular part in the apparatus in alignment with the seal units and with respect to the dies in the apparatus.
In the apparatus for hydroforming a tubular part, there is typically a lower die and an upper die that are pressed together to form a die cavity that extends about the part wherein the cavity has the shape to which the part is required to formed. In the hydroforming process, hydraulic fluid under pressure is delivered to the interior of the part through seal units that are associated with the lower die and are caused to engage opposite end portions of the part that project outward of the dies when the dies are closed about the part. To reduce cycle time, the seal units may be brought into sealing engagement with the ends of the part prior to the dies closing and it is important in that event that the ends of the part be accurately aligned with the seal units to effect their sealed engagement. As otherwise, proper sealing may not be obtained and the part and/or the seal units may be damaged.
In addition, the seal units may also be used to center the part lengthwise with respect to the dies prior to die closure through their engagement with the ends of the part. In that case, it is important that when the seal units are caused to engage with the ends of the part for such centering operation they do so in an efficient and reliable manner. Moreover, in the case where end portions of the part do project from the dies for engagement with the seal units, there is the possibility that the projecting end portions in an area where they are not captured by the seal units may burst during the hydroforming of the part and result in having to scrap the part.
An example of hydroforming apparatus that does provide for accurate alignment of projecting end portions of a round tubular part with the seal units is disclosed in U.S. Pat. No. 5,321,964 assigned to the assignee of this invention. As disclosed therein, each of the seal units is provided with a locator member and a backup member. The backup members are fixed with respect to the upper die and the locator members and their associated seal unit are mounted on separate elevators that are supported by springs with respect to the lower die. With the seal units retracted, the tubular part is loaded such as by a robot and at what will be its projecting end portions onto the locator members which locate the end portions in alignment with the respective seal units while the seal units and locator members are located and held by their respective elevator at an elevated position with respect to the lower die. The seal units are then extended to sealingly engage the respective end portions of the part while centering the part lengthwise with respect to the dies. The upper die is then lowered onto and pressed against the lower die to form the die cavity about the part. As the upper die is lowered to form the die cavity, this upper die movement also causes capture of the projecting end portions of the part between the respective locator and backup members as the dies are pressed together. This upper die movement also causes lowering of the elevators and thereby the part and the engaged seal units whereby an inward section of the end portions of the part ultimately seating on a terminal cavity bore portion in the lower die and in a corresponding terminal cavity bore portion in the upper die as the dies are pressed together.
While such apparatus has proven to provide satisfactory alignment of the part with the seal units, it has been found that because the end portions of the part are not fully radially restrained by the locator members of the respective seal units during the engagement of the seal units with the part prior to die closure, the part may bounce or be jostled and as a result interfere with the centering of the part with respect to the dies by the seal units and possibly result in damage to the part and/or the seal units.
In addition, the part as received from the tube manufacturer may have an outer diameter that is either undersize or oversize to a significant degree relative to the specified nominal dimension of the tube stock. As a result, these variations in dimensions can worsen the degree of bouncing and/or jostling that can occur when the seal units are advanced to engage the ends of the part to effect centering of the part between the dies and their sealing engagement therewith.
The present invention solves such problems by providing each seal unit with a tubular part locator comprising a locator member directly associated with the seal unit in a fixed relationship, a backup member rigidly fastened to the upper die and a pair of pivot arms which are mounted on the locator member and are operated by separate pneumatic cylinders. And wherein each seal unit and the associated locator member and pivot arms are mounted on an elevator.
The locator member has a concave surface and adjoining guide surfaces wherein the concave surface is of limited extent and conforms to the outer surface of the part and has a centerline coincident with that of the seal unit. And wherein the guide surfaces are adapted to guide an end portion of the part onto the concave surface of the locator member and thereby into alignment with the seal unit.
The pivot arms also have a concave surface conforming to the outer surface of the part but of substantially less extent than the concave surface of the locator member and are adapted on pivotal movement by their pneumatic cylinder to clamping positions to clamp the end portion of the part on the concave surface of the locator member to thereby prevent bouncing or jostling of the part while the seal unit is then brought into sealing engagement with the end portion of the part. The backup member also has a concave surface of limited extent conforming to the outer surface of the part and is adapted to move with the upper die to a backup position as the upper dies closes on the part where its concave surface then helps clamp the end portion of the part on the concave surface of the locator member.
The backup member when in its backup-clamping position is also adapted to hold the pivot arms in their clamping position during hydroforming of the part to thereby relieve the pneumatic cylinders of having to resist the hydroforming force acting in the end portion of the part outward on the pivot arms. Wherein there is provided a small predetermined clearance between the backup member and pivot arms that allows the end portion of the part to bulge slightly outward into hydraulically forced contact with the concave surfaces of the pivot arms and the backup member to assist in firmly holding the part in place. With there being a greater, but still a relatively small, amount of bulging allowed in the case of a nominal sized part and the smallest anticipated undersize part.
Moreover, the combined concave surfaces of the locator member, pivot arms and backup member completely encircle the end portion of the part between the dies and the respective seal unit and thereby act to prevent bursting of the end portion of the part during the hydroforming operation. In addition, the concave surfaces of the pivot arms and that of the backup member and the locator member are made slightly oversize by a predetermined amount with respect to the maximum anticipated outer diameter of the part as received from the tube manufacturer. Such that during the hydroforming of the part, the end portion regardless of its diameter bulges or expands slightly outward and tightly engages all these surfaces to help hold the part firmly in place.
Moreover, the components of the tubular part locator may be structured and arranged so as to allow the overall length and width of the seal unit including the part locator to be kept to a minimum. In addition, the tubular part locator lends its self to enhancing variations in certain of its components. For example, an optional pivot arm construction of short length that reduces the loading path of the part and thereby the cycle time for this operation. Another example is an optional convex funnel-shaped entryway in the locator member that also contributes to reducing loading time.